The present disclosure relates to a developing device in which developer is conveyed and an image forming apparatus provided with the same.
Conventionally, a developing device is known in which developer is conveyed in a circulating manner between a first conveyance path and a second conveyance path arranged in a developer housing. The developer is conveyed in opposite directions in the first and second conveyance paths by agitating screws arranged in the respective first and second conveyance paths. The agitating screw of the developing device is composed of a shaft portion and a spiral piece arranged around the shaft portion. In the developer housing, the developer is conveyed in a predetermined conveying direction by driving and rotating the agitating screws.
If an adhesion force of the developer increases as the developer is deteriorated, the developer may adhere to the shaft portion. If the developer adheres to the shaft portion, virtual shaft thickening of the agitating screw occurs to reduce the conveying performance of the agitating screw. An agitating screw including no shaft part, i.e. having a hollow shape in an axial central part thereof to solve the shaft thickening of the agitating screw described above is known.
With the agitating screw above described, developer conveying performance in an axial direction tends to be lower as compared with an agitating screw including a shaft portion extending in the axial direction. Thus, the transfer of the developer has not been preferably realized in communicating parts of the first and second conveyance paths at axial end parts of the agitating screws in some cases.
The present invention was developed in view of the above problem and an object thereof is to promote the transfer of developer in communicating portions in a developing device including developer conveying members having a hollow shape.